ON SOME GENETIC ASPECTS OF PHAGE Λ RESISTANCE IN E. COLI K12

Most mutations rendering E. coli K12 resistant to phage λ, map in two genetic regions mal A and mal B.—The malB region contains a gene lamB specifically involved in the λ receptor synthesis. Twenty-one independent lamB mutations studied by complementation belonged to a single cistron. This makes it very likely that lamB is monocistronic. Among the lamB mutants some are still sensitive to a host range mutant of phage λ. Mutations mapping in a proximal gene essential for maltose metabolism inactivate gene lamB by polarity confirming that both genes are part of the same operon. Because cases of intracistronic complementation have been found, the active lamB product may be an oligomeric protein.—Previously all λ resistant mutations in the malA region have been shown to map in the malT cistron. malT is believed to be a positive regulatory gene necessary for the induction of the "maltose operons" in the malA region and in the malB region of the E. coli K12 genetic map. No trans dominant malT mutation have been found. Therefore if they exist, they occur at a frequency of less than 10–8, or strongly reduce the growth rate of the mutants.